1. Field of the Invention
The invention relates to a drivable roll of controllable flexure, particularly for machines for the production and processing of paper or plastic webs.
2. Discussion of the Prior Art
Rolls of controllable flexure are basically known. U.S. Pat. No. 4,233,011, for example, the disclosure of which is hereby incorporated herein by reference, discloses a roll of this type comprising a substantially cylindrical inner part which through journals is firmly supported on a bearing surface, and a tubular outer part which surrounds the inner part and is supported at both ends on the inner part for rotation about the cylinder axis, there being disposed on the inner part along a generatrix means for generating compulsive forces acting radically between the inner part and the outer part. See FIG. 2 of U.S. Pat. No. 4,233,011.
In this non-driven prior-art roll of controllable flexure, unilateral heating of the inner part is utilized to secure a flexure of said part that is transmitted to the outer part since the latter is supported on the inner part. This makes it possible not only to compensate the natural deflection of the roll in order to achieve uniform contact pressure but also to secure in addition, for certain purposes, arching of the roll over given regions. It has now been found that practical problems will arise when a roll of controllable flexure is to be constructed as a drivable roll.
Drivable rolls of controllable flexure are also known per se.
For example, German Auslegschrift DAS No. 20 50 696, the disclosure of which is hereby incorporated herein by reference, describes a roll intended for high flexural loads in which a drive shaft which extends coaxially through one of the journals and in proximity to its outer end is supported on the journal is connected to a center gear which through a gear train mounted on the inner part drives an internal ring gear that is coaxial with the outer part and is in a driving relation therewith. In this prior-art roll, the gear train comprises two idler gears which are diametrically disposed in relation to the center gear and project through slots in the journal to mesh with the internal ring gear which is externally set onto and mounted on the end face of the outer part of the roll. To obtain troublefree operation of the drive even with pronounced deflection of the outer part of the roll, the center-gear shaft is not supported on the inner part of the roll but is connected to the drive shaft only through a flexible coupling. To provide for trouble-free operation of the drive, specified conditions must be satisfied with respect to the spacing of the center of the center gear from both the swivel point of the flexible coupling and the center of the self-aligning bearing between the outer and inner parts of the roll.
This prior-art roll has the drawback that it is of a rather complex design and expensive to produce,; and the two slots in the inner part through which the two idler gears project weaken that part considerably, thus limiting the maximum load it will sustain, unless it is overdimensioned. Moreover, since the center gear is connected to the drive shaft through a flexible coupling, the speed of rotation which can be transmitted, and hence the transmission ratio of the gear train, is limited. The center gear must be of relatively large size, which means high production costs and also requires a corresponding dimensioning of the journal. The high cost of this design is compounded by the fact that since the gear ratio is limited, relatively high torques must be transmitted to the gear train through drive shaft and flexible coupling. Moreover, making and maintaining the mentioned adjustment is complicated, and because of the disposition of the center gear and the manner in which it is connected, operation will be noisy, especially at higher rotative speeds. Finally, the torque must be transmitted from the internal ring gear mounted on the end face of the outer part to the outer part through interlocking connecting members, for example, bolted joints, which again poses adjusting and dimensioning problems.